The aim of this study has been the introduction and calibration of a novel Relative Humidity meter, based on optical
sensors. It consists of a psychrometer, whose temperature measurements are performed by means of two Fiber Bragg
Grating sensors, working as dry-bulb and wet-bulb thermometers. Their preliminary calibration permits to convert Bragg
wavelengths into temperature values with high repeatability and accuracy: hence, the local relative humidity can be
evaluated, using thermal gradient and dew point temperature, by a psychrometric table implemented as analytic function
inside a processing algorithm. The proposed sensor presents all the typical advantages of the optical devices, especially
the immunity to electromagnetic disturbances and to corrosion, allowing to measure humidity in aggressive
environments as meteorological off-shore stations, marine structures and vehicles.